The invention relates to an analog-to-digital conversion circuit comprising an analog-to-digital converter having an input and a plurality of outputs, a counter having counting position outputs to which are connected conversion circuit outputs for most significant bits of a signal converted by the conversion circuit, a digital-to-analog converter coupled to the counting position outputs and a difference threshold circuit coupled to an input of the conversion circuit and to an output of the digital-to-analog converter an output of the difference threshold circuit being coupled to the counter for applying thereto a threshold-crossing signal when the difference between an analog signal to be converted and the output signal of the digital-to-analog converter is too large.
U.S. Pat. No. 3,516,085 discloses an analog-to-digital conversion circuit of the above-mentioned type in which the difference between the input signal of the conversion circuit and the output signal of the digital-to-analog converter is applied to the input of the analog-to-digital converter and the output of the difference threshold circuit is connected to an input of the counter which determines whether the counter is to count up or down. When this counter is used, the number of bits in the output signal combination of the conversion circuit is increased without the necessity of extending the analog-to-digital converter.